Ozone, which causes photochemical smog, is produced by a photochemical reaction of HC and NOx contained in exhaust gases from vehicles and factories. Therefore, reducing the amount of emissions of HC and NOx from vehicles is an efficient way to suppress the production of ozone and the occurrence of photochemical smog. Also, purifying ozone in the atmosphere directly can be one of the ways to prevent the occurrence of photochemical smog. By purifying ozone as a product as well as reducing the amount of emissions of HC and NOx as reactants, the occurrence of photochemical smog can be prevented more effectively. In this respect, an vehicle including an atmosphere-cleaning device equipped on vehicle capable of directly purifying ozone in the atmosphere has been put into practical use in some places including California in the United States of America. This atmosphere-cleaning device equipped on vehicle, specifically, is called a DOR (Direct Ozone Reduction) system.
For example, Patent Literature 1 discloses a DOR system in which a metal oxide such as manganese dioxide is supported by an on-vehicle component. An on-vehicle component such as a radiator is disposed at a spot in contact with atmosphere during travel of the vehicle, and manganese dioxide has a function of converting ozone contained in the atmosphere into other substances such as oxygen, and purifying ozone. Therefore, according to the DOR system disclosed in Patent Literature 1, ozone in the atmosphere can be directly purified during travel of the vehicle.